1. Field of the Invention
The invention relates to a frequency selective optical data record/regenarate apparatus.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a configuration of a conventional frequency selective optical data record/regenerate apparatus, for example, shown in the Japanese Patent Publication No. 51355/1983, and FIG. 2 is a wavelength spectral diagram of a medium wherein information is recorded. As shown in FIG. 1, light emitted from a wave-length-variable light source 81 becomes parallel light by a collimator lens 83, and is deflected in a predetermined direction by an optical deflector 84. Thereafter it becomes a minute light spot by an objective lens 85, and is projected onto a required memory element 87 on a medium 86 having a function of frequency selective optical data record/regenerate, and the light passing through the memory element 87 is detected by a photo detector 88 installed opposite to the light source 81 through the medium 86. The memory element 87 whereto light is to be projected is selected freely by deflecting the light spot by the optical deflector 84. Also, the wavelength of the light source 81 is varied by a wavelength controller 82 of a scanner or the like installed outside the light source 81.
Description is made on the principle of record and regeneration by means of multiple-wave-length system on the basis of FIG. 2. FIG. 2 (a) shows absorption spectra of the medium 86 before multiple-wavelength record, and the medium 86 has a broad spectral characteristic. when light having spectra of light intensity as shown by broken lines in FIG. 2 (a) is projected to this medium 86, dips are produced at the absorption spectra of the projected wavelengths as shown in FIG. 2 (b), and this dip is called a spectral hole (hereinafter referred to simply as hole). When the hole is produced, data "1" is assumed to be recorded at this wavelength, and the place without the hole is assumed as data "0". To form the hole at an arbitrary wavelength (in other words, write data "1"), the wavelength of the light source 81 is tuned by the wavelength controller 82 to the wavelength at which the hole is wanted to be formed, and further the light intensity of the light source 81 is raised to a light intensity required for record. To read a signal from the medium having the spectra multiple-recorded by forming the holes at different wavelengths as shown in FIG. 2 (b), the medium 86 is scanned by the wavelengths covering a wavelength region from A to B, with the light intensity of the light source 81 is kept constant, and thereby since the absorption factor is reduced at the wavelength where the hole is produced as shown in FIG. 2 (b), the photo detector 88 detects the light transmitted through the medium 86, and spectra of light intensity as shown in FIG. 2 (c) is obtained. Accordingly, by scanning the record position while varying at a constant speed the wavelength in the wavelength region used for storage, regeneration signals on a wavelength basis showing presence or absence of the holes are obtained from output of the photo detector 88. Also, if the varying speed of the wavelength is constant, time series regeneration signals of the stored data are obtained as the output of the photo detector 88.
Also, the number of the holes n which can be formed at the absorption spectra of the wavelength region from A to B, is roughly shown by the following equation. ##EQU1## In equation (1), .DELTA.W.sub.I is the band width of absorption spectra and .DELTA.W.sub.H is the width of one hole. Accordingly, the number of the holes n which can be formed increases with decrease in the value of .DELTA.W.sub.H, and generally the value of .DELTA.W.sub.H decreases with decrease in temperature, while .DELTA.W.sub.I is hardly affected by temperature, and therefore the number of holes n which can be formed, in other words, the data storage capacity wherein one hole is equivalent to one bit increases at lower temperatures.
This means that in the conventional frequency selective optical data record/regenerate apparatuses, information recorded by the same wavelength is multiple-recorded on a wavelength basis, and the multiple-recorded information is regenerated by a required single wavelength.
Then, products oscillating reliably at a required wavelength have not been obtained yet by the current level of manufacturing technology for the light source such as semiconductor laser, and the oscillation wavelength is varied also by effects of temperature and the like, and therefore some wavelength controlling means is required to be provided. Accordingly, in the conventional frequency selective optical data record/regenerate apparatuses, the oscillator wavelength is controlled by a controller installed outside the light source, and therefore miniaturization of the optical system is difficult to be realized.
Also, since the controller continuously varies the oscillation wavelength of the laser, each wavelength cannot be separated clearly from the other wavelengths, and thus the problem of low precision of record and regeneration is left unsolved.